Municipal water demand is quite variable. It is very low around midnight and extremely high at other times - such as when lots of toilet are flushed during Super Bowl halftime. It would be very expensive and impractical for the city to size the water supply pumps for this maximum flow. Instead, they use smaller pumps to fill a water tower or a tank on a hill with a much lower steady flow. Demand surges are supplied by the water stored in the tower or tank.

Engine air demand is unsteady, too. The intake valve is open and passing mixture for only a small part of the engine cycle. The rest of the time it is shut. The air filter is mounted directly to the carb now. This is a lousy setup. Their is a very small reservoir of air beyond the air intake for the engine to draw from. It is the inside volume of the filter. The filter is subject to pulsing flow demands. These can be quite large. It is a filter on a 500cc single cylinder engine turning 10,000 rpm, in reality.

A plenum will be made along with the new stack and it will be sized to provide a reservoir of air in front of the filter. The minimum volume will be the cylinder volume x the maximum volumetric efficiency. It will store at least one gulp of air between the bell mouth and the filter. This will reduce peak flow loads on the filter and reduce any restriction the filter might provide during those peaks. In addition, the two plenums will be connected so the reservoir is larger.

One thing governing the stack size is the need to keep it at least 1/4 inch from and plenum wall. This will promote more a more even inflow rate around the stack perimeter. This is a problem with this bike I have known about for a decade. Right now I am finding the time to fix it.

Wobbley, calculations tell me that at 160mph one would see about .44 psi in plenum if ram air is used,, your considerations ??

My first bike was a new '69 Yamaha 250 DT-1 and I was 17 or 18 years old during Projekt Ram Air. The engine had Yamaha GYT kit internals with a Schwerma expansion chamber. My buddies and me made a ram air system and could not make it work. The problem was the main jet size. It needed to be larger than it would be without a pressurized air box. The exact size was variable. It would be different when the bike was topped out in third, fourth, or fifth 'cause ram air pressure differed at varying speeds. Also, ram air pressure changed drastically when running against or with the wind. A hole in the piston due to a lean mixture put an end to that project. What I learned was, it is cheapest to figure things out on a single cylinder engine and to stay away from ram air with a carb fed motor. Maybe the folks with EFI have figured out a way to get the mixture correct. It was prehistoric times back then. Carbs was all we had.

My first bike was a new '69 Yamaha 250 DT-1 and I was 17 or 18 years old during Projekt Ram Air. The engine had Yamaha GYT kit internals with a Schwerma expansion chamber. My buddies and me made a ram air system and could not make it work. The problem was the main jet size. It needed to be larger than it would be without a pressurized air box. The exact size was variable. It would be different when the bike was topped out in third, fourth, or fifth 'cause ram air pressure differed at varying speeds. Also, ram air pressure changed drastically when running against or with the wind. A hole in the piston due to a lean mixture put an end to that project. What I learned was, it is cheapest to figure things out on a single cylinder engine and to stay away from ram air with a carb fed motor. Maybe the folks with EFI have figured out a way to get the mixture correct. It was prehistoric times back then. Carbs was all we had.

My experience with ram air has only been with the efi bikes where the ecu compensates for a/f demands,, I had overlooked the fact that your bike is carburated,,

my thoughts with carbies and ram air would be that you would control the fuel demands with the needle,,

I run ram-air with carbs on my CB750...........it works ...........the bowl-vents have to be connected to the air-box for balanced internal pressure. The science is simple............at speed you are likely to be losing some amount of available air due to the sweeping vacuum effect of the passing air. The ram-air merely provides 100% or very slightly more.............but you need a large volume air-box between the filter and carb-intake.

Another benefit from ram-air is the somewhat cooler and 'clean' air obtained at the front of the bike. Pssst!......flat-sided air-ways flow better than round, and also allow more air to enter the inlet, therefore; smaller runners with square corners will flow more air than a round tube......and much, much more than a corrigated tube.

This is how the ellipse was cut. First, it was drawn out on graph paper at a 10:1 scale. Ten inches on the paper equaled an inch on the part. The book that showed me how to do this is "Engineering Graphics" ISBN 0-02-342720-5. It is a good reference for a fabricator to have. Type "draw ellipse trammel method" into Google and references showing it will appear. That was how I drew it.

A cut schedule was made using the drawing, protractor, and scale. Each cut was plotted out and so I knew the angle of the cut and its width.

The cut area was coated with machinist dye and the cut was made at the same width as indicated by the drawing. A decimal machinist scale made this easy. A 0.75 inch wide cut scaled on the drawing was a 0.075 inch wide cut on the part. The part was roughed out on the lathe by many cuts using the tool bit and it was sanded down to final size using emery cloth.